1. Field of the Invention
This invention relates to a solid catalyst component for use in the polymerization of .alpha.-olefins. More particularly, this invention relates to a solid catalyst component for use in the polymerization of .alpha.-olefins, which is quite excellent in catalytic activity and stereospecificity and improved in resistance to grinding, characteristics of particles and convenience in handling.
2. Description of the Prior Art
As a general process for producing a polymer of .alpha.-olefin such as propylene, butene-1 and the like, the use of the so-called Ziegler-Natta catalyst consisting of a compound of transition metal belonging to Group IV-VI of the periodic table and an organometal compound belonging to Group I-III of the periodic table is well known.
In such a production process, however, an amorphous polymer is formed as a by-product in addition to a highly stereospecific .alpha.-olefin polymer having a high industrial value.
The amorphous polymer is low in industrial utilizability and exercises a very adverse influence upon mechanical properties of the .alpha.-olefin polymer when the polymer is processed into film, fiber and other forms and put to use.
Further, formation of the above-mentioned amorphous polymer causes a loss of starting monomer and makes it indispensably necessary to provide an apparatus for removing the amorphous polymer, which is quite disadvantageous from the industrial point of view.
Accordingly, if a process entirely free from formation of such an amorphous polymer or a process for forming only a slight quantity of amorphous polymer is discovered, it will be quite advantageous.
On the other hand, in such a polymerization process as above, catalyst residue remains in the resulting .alpha.-olefin polymer, which makes troubles in various points such as stability, processability, etc. of the .alpha.-olefin polymer. Thus, it is necessary to provide an apparatus for removing the catalyst residue and stabilizing the polymer.
This fault can be overcome by increasing the catalytic activity expressed by the weight of formed .alpha.-olefin polymer per unit weight of catalyst. By this increase, the apparatus for removing catalyst residue becomes unnecessary and production cost of .alpha.-olefin polymer can be reduced.
The present inventors previously proposed a process which comprises treating, with an ester compound, an ether compound and titanium tetrachloride, a solid product obtained by reducing an alkoxytitanium compound with an organomagnesium compound in the presence of an organic silicon compound having Si--O bond [U.S. Pat. 4,672,050, Japanese Patent Application KOKAI (Laid-Open) No. 1-319508]. The catalyst obtained according to this process could overcome the above-mentioned fault in stereospecificity and catalyst activity.
The solid catalyst component obtained by the above-mentioned process is usually dried until it reaches a fluidizable state and thereafter put to use, for the reason of convenience for use, in many cases.
As a drier used for drying powdery materials, various driers have been proposed. For example, as material-standing and material-conveyance type driers; vacuum box type drier, freeze dried box type drier, ordinary pressure drum drier, vacuum drum drier, vertical drier, cylindrical drier, band drier and the like can be referred to. As material-agitation type driers; ventilation rotary drier, ventilation agitation drier, fluidized bed drier, cylindrical agitation drier, multi-stage disc drier, grooved agitation drier and the like can be referred to. Further, as hot air conveyance type driers, spray drier, air stream drier and the like can be referred to. A variety of driers constituted of combination of these driers are also used. In the case of a solid catalyst component for olefin polymerization which must be handled in an inert gas and made free from organic solvent by a drying process, there are often used driers in which ventilation and agitation are combined such as ventilation rotary drier, ventilation agitation drier, gas stream drier and fluidized bed drier, with consideration of safety, convenience in handling and cost.
However, a solid catalyst component obtained by the above-mentioned process has a problem that fine powder is formed by friction between particles in the process of drying treatment accompanied by powder flow. Such a solid catalyst component containing fine powder deteriorates the particle size distribution of the resulting .alpha.-olefin polymer which copies the shape of the solid catalyst component, and thereby forms a fine powdery polymer. Further, the fine powder agglomerates in the course of polymerization to clog the lines of polymer-producing apparatus and makes it impossible to produce a polymer stably. Accordingly, elimination of such a fine powder from the solid catalyst component will bring about a great merit.
As a technique for improving the crushability of solid catalyst component, there has been disclosed a method which comprises preliminarily polymerizing an olefin in the presence of a solid catalyst component and thereby preventing the formation of fine powder at the time of supplying a slurry of the solid catalyst component into polymerization reactor by means of a circulating pump [Japanese Patent Application KOKAI (Laid-Open) No. 57-151602]. However, such a method has a problem that the solid catalyst component comes to coexist with an organoaluminum compound during the period from completion of preliminary polymerization to its feeding into the polymerization reactor and, during this period of storage, its activity is deteriorated with the lapse of time. Further, there has been disclosed a method [Japanese Patent Application KOKAI (Laid-Open) No. 63-89509]which comprises inserting a step of preliminary polymerization of .alpha.-olefin into the step of synthesizing a solid-catalyst component and thereafter treating the catalyst component with a titanium compound to obtain a solid catalyst component in order to prevent the pulverization of the particles of solid catalyst component in the course of synthesizing the solid catalyst component. However, even if such a method is applied to the technique previously proposed by the prior arts [U.S. Pat. No. 4,672,050, Japanese Patent Application KOKAI (Laid-Open) No. 1-319508], the preliminarily polymerized polymer dissolves into solvent at the time of treating the solid catalyst component with a titanium compound and filtration cannot be effected satisfactorily or the remaining organoaluminum compound reacts with the titanium compound to form an undesirable compound decreasing the polymerization activity and stereospecificity.